Electrical generators are used in a wide variety of applications. Typically, an individual electrical generator operates in a stand-by mode wherein the electrical power provided by a utility is monitored such that if the commercial electrical power from the utility fails, the engine of the electrical generator is automatically started causing the alternator to generate electrical power. When the electrical power generated by the alternator reaches a predetermined voltage and frequency desired by the customer, a transfer switch transfers the load imposed by the customer from the commercial power lines to the electrical generator. As is known, most residential electric equipment in the United States is designed to be used in connection with electrical power having a fixed frequency, namely, sixty (60) hertz (Hz).
Typically, electrical generators utilize a single driving engine coupled to a generator or alternator through a common shaft. Upon actuation of the engine, the crankshaft rotates the common shaft so as to drive the alternator that, in turn, generates electrical power. The frequency of the output power of most prior electrical generators depends on a fixed, operating speed of the engine. Typically, the predetermined operating speed of an engine for a two-pole, stand-by electrical generator is approximately 3600 revolutions per minute to produce the rated frequency and power for which the unit is designed. However, in situations when the applied load is the less than the rated kilowatt load for which the unit is designed, the fuel-efficiency of the engine will be less than optimum. As such, it can be appreciated that it is highly desirable to vary the operating speed of the engine of an electrical generator to maximize fuel efficiency, and thus reduce CO2 emissions, of the engine for a given load. Further, operation of the engine-driven, electrical generator at its predetermined operating speed can produce unwanted noise. It can be appreciated that reducing the operating speed of the engine of an electrical generator to correspond to a given load will reduce the noise associated with operation of the engine-driven, electrical generator.
Operating the engine at a reduced speed does, however, have certain drawbacks. Operation at a reduced speed results in a lower power output from the generator. Further, the load applied to the generator may change after the initial determination of an optimum operating speed. For example, a sump pump, a furnace, or another electrical load may be switched on, creating an additional power demand on the generator. Even if the additional demand may be within the capacity of the generator system when the engine is operating at maximum speed, the additional demand may be in excess of the capacity of the generator when it is operating at the reduced speed. If the change in the power demand is too great, it may cause the engine to begin to slow and/or to stall.
Therefore, it is a primary object and feature of the present invention to provide a method for rapidly detecting a change in the power demanded from the generator system as a result of an additional load being applied to the generator system.
It is another primary object and feature of the present invention to provide a method that allows the engine to accelerate to maximum speed and, thereby, generate maximum power such that the generator system may provide power to the new load.
In accordance with the present invention, a method of controlling an engine-driven, electrical generator system configured to generate an alternating current (AC) power at a desired output frequency for multiple electrical loads is disclosed. A value of the AC power output by the generator system is determined at least once during each electrical cycle of the AC power. A change in the value of the AC power output greater than a preset threshold is detected, and a switch is opened to disconnect at least one of the electrical loads from the generator system responsive to detecting the change in the value of the AC power output greater than the preset threshold. The engine is accelerated to a maximum operating speed, and the switch is closed to reconnect the electrical load to the generator system.
According to another aspect of the present invention, the generator system outputs a control signal responsive to detecting the change in the value of the AC power output, and the control signal is provided to the switch to open and close the switch. The step of detecting the change in the value of the AC power output may be done within two electrical cycles of the AC power. The engine may operate at the maximum operating speed for a predefined time after accelerating to the maximum operating speed, and the operating speed of the engine may be varied as a function of the fuel consumption of the generator system upon completion of the predefined time. Further, the value of the AC power output may be determined by a calculation of real power, apparent power, or a combination thereof.
According to another embodiment of the invention, a method of controlling an engine-driven, electrical generator system is disclosed. The engine of the generator system is configured to operate at an engine speed and the generator system is configured to generate an alternating current (AC) power having a desired output frequency. The method includes the steps of running the engine at a first engine speed, connecting a load to an output of the generator system, and detecting a change in the value of the AC power output greater than a preset threshold within two electrical cycles of the AC power. Optionally, a decrease in the engine speed greater than a preset threshold may be detected. After detecting either the change in the value of the AC power output or the decrease in the engine speed, at least a portion of the load is disconnected from the output of the generator system. The engine is accelerated to a maximum operating speed, and the disconnected portion of the load is reconnected to the output of the generator system.